The present invention relates to a developer concentrate capable of dilution with tap water to a ready-to-use state, which concentrate is suitable for developing negative-working exposed reproduction layers in copying materials, and also to a process for producing printing forms.
Copying materials of the above-mentioned type are used, in particular, in producing printing plates or photoresists and are composed of a layer base and a negative-working, photosensitive reproduction layer. The layer bases used in these copying materials comprise metals such as zinc, chromium, copper, brass, steel, aluminum or combinations of these metals, plastic sheets, paper or similar materials. The layer bases may be coated with the photosensitive reproduction layer without a modifying pretreatment; however, the layer bases preferably are coated after carrying out a surface modification such as a mechanical, chemical or electrochemical roughening, an oxidation and/or a treatment with hydrophilizing agents (for example, in offset printing plate bases). The reproduction layer includes water-insoluble diazonium salt polycondensation products.
In addition to photosensitive components, the reproduction layer may also contain plasticizers, pigments, dyestuffs, wetting agents, sensitizers, indicators and other standard auxiliaries. Such reproduction layers are described comprehensively, for example, in U.S. Pat. No. 3,867,147.
Known developers or developer mixtures have, in particular, the following disadvantages:
they often contain fairly high proportions of organic solvents which should, if possible, no longer be present in modern developers for ecological drawbacks such as a low boiling point, fire hazard, unpleasant smell, adverse effect on waste water and exhaust air and expensive precautions for eliminating the solvents after development; PA1 although lauryl sulfate or other alkyl sulfates or alkane sulfonates often used in conventional practice are, per se, effective developer components for the specified photosensitive reproduction layers, they require a comparatively long development time, they foam too extensively in processing machines, in particular in the case of vertical development, and the solubility in water at low temperatures (for example, from about 10.degree. C. and lower) decreases to an extent such that, at autumn or winter temperatures, flaky residues which are often troublesome for the processor may be produced in the stock solutions. Spots of grease and adhesive residues such as may occur in handling offset printing plates under practical conditions are removed by these developer components at best after a long action time and by additional mechanical aids; PA1 although lauryl sulfate or other alkyl sulfates or alkane sulfonates are frequently suitable when used for the specific reproduction layers for which they were developed and with which they are also successfully used in the respective examples, they exhibit more or less considerable difficulties with layers which are different from these specific reproduction layers, i.e., they cannot be employed universally. PA1 they also are unsuitable in general for suppressing the impurities (flakes and filaments) which are encountered in many cases, mainly in mechanical development, and which settle as redeposits on the printing forms, with the result that optimum quality of the final product cannot be achieved, even when the developer is used for a long time. PA1 has a high solids content and also exhibits no precipitates, phase separations or turbidities on thawing even after a fortuitous freezing, PA1 can, if necessary, be diluted before use in the printing shop with water containing Ca and Mg ions, in particular tap water, to the extent necessary in practice without precipitates appearing in the process, PA1 develops rapidly and in doing so has equally ideal development properties (good resolution of the non-image areas and non-attack of the image areas) in order to enable it to be used in automatic processing systems, PA1 develops either as a concentrate or in the various degrees of dilution without flake and filament formation and at the same time has a high economy in use, i.e., can be used even over a prolonged period of time in its development capacity without forming contaminants, and PA1 can be used either with binder-containing or with binder-free systems. PA1 X is the anion of the diazonium compound, PA1 p is an integer from 1 to 3, PA1 R.sup.8 is an aromatic radical having at least one position capable of condensation with an active carbonyl compound, PA1 R.sup.10 is a phenylene group, and PA1 R.sup.9 is a single bond or one of the following groups: PA1 q is a number from 0 to 5, PA1 r is a number from 2 to 5, PA1 R.sup.11 is hydrogen, an alkyl group having 1 to 5 carbon atoms, an aralkyl group having 7 to 12 carbon atoms or an aryl group having 6 to 12 carbon atoms, and PA1 R.sup.12 is an arylene group having 6 to 12 carbon atoms.
U.S. Pat. No. 4,716,098 describes a developer mixture which is different from the prior art described above, does not exhibit the disadvantages thereof and is suitable for developing lithographic printing plates. The layers described therein include a diazonium salt polycondensation product and an alkali-soluble binder which contains carboxyl groups. However, this developer mixture is stable only in very dilute form and therefore exists only in dilute aqueous solution. Specifically, developer includes up to 85% water, as a result of which unnecessarily large containers which have adverse effects on transport and application are needed. Based on the examples described in U.S. Pat. No. 4,716,098, an attempt was made to prepare a concentrate by not adding some of the water in the case of the developer mixtures mentioned therein. It emerged, however, that the components of all the examples no longer dissolve homogeneously and phase separations occur or precipitates appear on freezing which are also no longer reversible after thawing.